The invention relates to apparatus for building a stream of fibrous material, particularly to improvements in apparatus for building a stream which contains or consists of tobacco particles. Still more particularly, the invention relates to improvements in apparatus for building a stream of fibrous material which is to be draped in cigarette paper or other relatively thin and weak wrapping material such as is likely to be damaged as a result of contact with relatively hard and/or relatively sharp particles.
As used herein, the term "tobacco" is intended to denote natural, artificial and reconstituted tobacco as well as all forms of natural tobacco including tobacco leaves, tobacco leaf laminae, tobacco ribs as well as fragments of tobacco leaves, laminae and ribs. The following description will deal primarily with the making of tobacco streams which are to be converted into the fillers of cigarette rods. However, the invention can be practiced with equal or similar advantage in connection with the making of streams which are to be converted into rod-like fillers of cigars, cigarillos and/or other rod-shaped smokers' products.
The making of cigarettes normally involves preliminary treatment of tobacco particles and introduction of such particles into the distributor (also called hopper) of a rod making machine. The distributor furnishes a relatively wide and relatively thin layer or carpet of loosened tobacco particles, and such carpet is then conveyed against the underside of the lower reach of an endless foraminous belt conveyor which cooperates with a suction chamber to gather a stream containing a surplus of tobacco particles. The surplus is removed by a so-called trimming or equalizing device, and the thus obtained rod-like filler (trimmed tobacco stream) is draped into a web of cigarette paper to form a cigarette rod which is severed by a so-called cutoff to yield plain cigarettes of unit length or multiple unit length.
In many or most instances, the carpet of loosened tobacco particles contains shredded tobacco leaf laminae as well as fragments of tobacco ribs. The fragments of ribs are normally heavier and harder than the shreds of tobacco leaf laminae; therefore, the distributor of a cigarette rod making machine normally comprises one or more classifying devices which segregate fragmentized tobacco ribs from shreds of tobacco leaf laminae because the fragments of ribs are highly likely to puncture and/or otherwise damage the tubular envelope consisting of cigarette paper or other wrapping material which is used to surround the trimmed or equalized tobacco stream. It has been found that even repeated classifying of tobacco particles in the distributor is not likely to result in segregation of all or practically all fragments of tobacco ribs, i.e., the cigarette rod is likely to embody a tubular wrapper which is punctured at one or more locations to permit uncontrolled escape of tobacco smoke and/or uncontrolled flow of air into the rod-like tobacco filler of a cigarette, be it a plain cigarette or a filter cigarette. In either event, the presence of holes in the wrappers of plain or filter cigarettes is irritating to the smoker and detracts from the appearance and other desirable qualities of the ultimate product.